1. Field of the Invention
The present invention relates to electrochemical energy converters with a polymer electrolyte membrane (PEM), such as fuel cells or electrolyzer cells or stacks of such cells, wherein the individual cells are modular units which have integrated the bipolar separator plate (BSP), the membrane electrode assembly (MEA) and the reactant and coolant manifolds. These individual components are assembled into integrated modules and these modules are tested individually for full functionality before being assembled into a complete fuel cell unit (stack) as individual components. In particular the several components of the integrated modular BSP/MEA/Manifolds (fuel cell module), i.e., the bipolar separator plate, membrane electrode assembly, separate diffusion layers (if used), gaskets (if used), manifolds, adhesives, and seals (if used) are manufactured as separate entities before being incorporated into a fuel cell module before being assembled in a complete fuel cell unit (stack). In a number of embodiments, these fuel cell components can be as large or as small as the end use requires.
2. Description of the Related Art
Electrochemical cells comprising polymer electrolyte membranes (PEM) may be operated as fuel cells wherein a fuel and an oxidizer are electrochemically converted at the cell electrodes to produce electrical power, or as electrolyzers wherein an external electrical current is passed between the cell electrodes, typically through water, resulting in generation of hydrogen and oxygen at the respective electrodes of the cells.
Fuel cells are energy conversion devices that use hydrogen, the most abundant fuel on earth, and oxygen, usually from the air, to create electricity through a chemical conversion process, without combustion and without harmful emissions. The voltage and current output depends on the number of cells in the stack, total active surface area and efficiency. The basic process, for a single cell, is shown in FIG. 1.
Traditional fuel cell stacks 1, see FIG. 2, are made of many individual cells 2, see FIG. 3, which are stacked together. The ability to achieve the required gas and liquid sealing and to maintain intimate electrical contact has traditionally been accomplished with the use of relatively thick and heavy “end plates” (3, 4) with the fuel cell stack 5 held together by heavy tie-rods or bolts 6 and nuts 7 (or otherfasteners) in a “filter-press” type of arrangement, see FIGS. 2 and 4. Disassembly and analysis of fuel cell stacks built by traditional and other methods reveals evidence of incomplete electrical contact between bipolar separator plates (BSPs) 8 and the membrane electrode assembly (MEAs) 9, which results in poor electrical conduction, lower cell performance, often along with evidence of gas and liquid leakage.
The traditional method of assembly of Proton Exchange Membrane (PEM) fuel cells requires several parallel and serial mechanical processes that must be accomplished simultaneously for each individual cell, see FIG. 3.
1. The Membrane Electrode Assembly (MEA) 9 must be sealed to the Bipolar Separator Plates (BSPs) 8 at each plate/MEA interface, via a gasket such as 10A and 10B.
2. The fuel, oxidizer and coolant manifolds 11A and 11B are all required to be sealed at the same time during fabrication as the MEA is sealed to the BSP.
3. The BSPs 8 must be in intimate electrical contact with the electrode assembly 9, across its entire surface area, at all times for optimum performance. As the traditional fuel cell stack 1 is assembled, each individual cell (layer) 2 must seal, manage gasses and liquid, produce power and conduct current. Each cell relies on all the other cells for these functions. Additionally, all seals and electrical contacts must be made concurrently at the time of assembly of the stack, see FIGS. 2 and 3.
The assembly of a traditional PEM cell stack which comprises a plurality of PEM cells each having many separate gaskets which must be fitted to or formed on the various components is labor-intensive, costly and in a manner generally unsuited to high volume manufacture due to the multitude of parts and number of assembly steps required.
With the conventional PEM stack design 1, see FIG. 2, it is problematic to remove and repair an individual cell 2 (see FIG. 3) or to identify or test which cell or cells in the stack may require repair due to leakage or performance problems. In many cases the entire stack assembly is required to be dissembled. The disassembly of a stack consisting of multiple cells, each comprising separate cell components can be very costly as in many instances, after the removal of one cell, the gaskets of the remaining cells may need to be replaced before the stack can be reassembled and operated. Additionally, the potential for damage to the MEA is very high. Upon reassembly, there is no assurance of the performance or of a leak tight condition. This is a very time consuming and therefore costly process.
Some patents of interest are listed below.
R. G. Spear, et al. in U.S. Pat. No. 5,683,828, assigned to H Power Corporation disclose metal platelet fuel cells production and operation methods.
R. G. Spear, et al. in U.S. Pat. No. 5,858,567, assigned to H Power Corporation disclose fuel cells employing integrated fluid management platelet technology.
R. G. Spear, et al. in U.S. Pat. No. 5,863,671, assigned to H Power Corporation disclose plastic platelet fuel cells employing integrated fluid management.
R. G. Spear, et al. in U.S. Pat. No. 6,051,331 assigned to H Power Corporation disclose fuel cell platelet separators having coordinate features.
These four U.S. patents to Spear et al. describe conventional fuel cell assembly.
W. A. Fuglevand, et al. in U.S. Pat. No. 6,030,718, assigned to Avista Corporation disclose a proton exchange membrane fuel cell power system.
D. G Epp, et al. in U.S. Pat. No. 5,176,966 disclose a fuel cell membrane electrode and a seal assembly.
W. J. Fletcher, et al. in U.S. Pat. No. 5,470,671 disclose an electrochemical fuel cell which employs ambient air as both oxidant and coolant.
W. D. Ernest, et al. in U.S. Pat. No. 5,945,232 disclose a PEM-type fuel cell assembly having multiple parallel fuel cell sub-stacks employing shared fluid plate assemblies and shared membrane electrode assemblies.
R. A. Mercuri, et al. in U.S. Pat. No. 5,976,727 disclose an electrically conductive seal for fuel cell components.
R. D. Breault, et al. in U.S. Pat. No. 6,020,083 disclose a membrane electrode assembly for a PEM fuel cell.
R. H. Burton, et al. in U.S. Pat. No. 6,057,054 disclose a membrane electrode assembly for an electrochemical fuel cell and a method of making an improved membrane electrode assembly.
J. A. Ronne, et al. in U.S. Pat. No. 6,066,409 disclose an electrochemical fuel cell stack with improved reactant manifolding and sealing.
O. Schmidt et al. in U.S. Pat. No. 6,080,503 disclose polymer electrolyte membrane fuel cells and stacks with adhesively bonded layers.
Other art of general interest includes, for example: U.S. Pat. No. 5,338,621; European Patent 446,680; U.S. Pat. Nos. 5,328,779; 5,084,364; 4,548,675 and 4,445,994.
All of the references, patents, patent applications, standards, etc. cited in this application are incorporated by reference in their entirety.
With reference to FIG. 3 and Claims 1 and 2 of U.S. Pat. No. 6,080,503 which is incorporated herein by reference, the adhesive bonding agent used is for bonding “a first separator plate” and “a second separator plate” to a membrane electrode assembly”, in the current embodiment a single separator plate is bonded to a single MEA and to manifolds which are external to the membrane assembly with no through passages holing the membrane. This embodiment forms a fuel cell module (assembly).
It is apparent from the above discussion that existing fuel cell technology can be significantly improved using modular components and in the assembly of the multiple fuel cell unit (stack). This invention concerns an improved, integrated and modular BSP/MEA/Manifold assembly, which facilitates single cell (module) leak and performance testing prior to assembly. It also eliminates gaskets between adjacent BSP and simplifies assembly. The present invention of modular, integrated units provides such improvements for a fuel cell.